Control system for a sealed coolant flow field fuel cell power plant having a water reservoir

Abstract

The system ( 10 ) controls at least one of a pressure of the reactant streams ( 16 A, 16 B) within at least one of an anode flow field ( 28 ) and a cathode flow field ( 36 ), a flow rate of the reactant streams ( 16 A, 16 B) flowing through the anode and/or cathode flow fields ( 26, 28 ), a temperature of a coolant fluid passing through a sealed coolant flow field ( 44 ), and a flow rate of the coolant fluid; so that water ( 14 ) moves from a water reservoir ( 18 A, 18 B) into the reactant stream ( 16 A, 16 B) whenever power generated by the fuel cell ( 20 ) is between about 80% and about 100% of a maximum fuel cell power output, and so that water ( 14 ) moves from the reactant stream ( 16 A, 16 B) into the water reservoir ( 18 A, 18 B) whenever fuel cell power is less than about 75% of the maximum power output.

What is claimed is: 
     
       1. A control system of a fuel cell power plant configured to generate electrical current from an oxidant reactant stream and a hydrogen-rich fuel reactant stream, the control system comprising:
 at least one fuel cell including a membrane electrode assembly having a proton exchange membrane disposed between an anode catalyst surface and an opposed cathode catalyst surface of the assembly, an anode flow field defined in fluid communication with the anode catalyst surface and with a fuel inlet line to direct flow of the hydrogen-rich fuel reactant stream from the fuel inlet line adjacent the anode catalyst surface and out of the anode flow field through an anode exhaust as an anode exhaust stream, a cathode flow field defined in fluid communication with the cathode catalyst surface and with a source of the oxidant to direct flow of the oxidant reactant stream from an oxidant inlet line adjacent the cathode catalyst surface and out of the cathode flow field through a cathode exhaust as a cathode exhaust stream; 
 a sealed coolant flow field secured in thermal exchange with one of the anode flow field and the cathode flow field for directing to direct a coolant fluid from a coolant inlet of a coolant loop, through the coolant flow field and through a coolant loop outlet, the coolant loop configured to control a temperature of the coolant fluid within the coolant flow field; 
 at least one water reservoir secured in fluid communication with at least one of the anode flow field and the cathode flow field and secured in fluid isolation from the sealed coolant flow field, the water reservoir configured to move water from the reservoir and into the reactant stream located in the at least one of the anode and cathode flow fields, and to move water from the reactant stream located in the at least one of the anode and cathode flow fields and into the at least one reservoir; and, 
 a relative-humidity controller secured in communication with the fuel cell and configured to selectively control at least one of a pressure of the reactant streams, a flow rate of the reactant streams, and a temperature of the coolant fluid within the sealed coolant flow field, so that water moves from the water reservoir into the reactant gas streams whenever power generated by the fuel cell is between about eighty percent and about one-hundred percent of a predetermined maximum power output of the fuel cell, and so that water moves from the reactant gas streams into the water reservoir whenever power produced by the fuel cell is less than about seventy-five percent of the predetermined maximum power output of the fuel cell. 
 
     
     
       2. The control system of  claim 1  further comprising a relative-humidity sensor secured in communication with the reactant stream passing through the at least one of the anode flow field and the cathode flow field, and also secured in communication with the relative-humidity controller to communicate sensed information about the relative humidity of the reactant streams to the controller. 
     
     
       3. The control system of  claim 2 , wherein the relative-humidity sensor is secured in communication with the cathode exhaust. 
     
     
       4. The control system of  claim 1  wherein the relative-humidity controller is also secured in communication with at least one of a fuel inlet valve secured to the fuel inlet line, an oxidant inlet valve secured to the oxidant inlet line, an oxidant blower-secured to the oxidant inlet line, an anode exhaust valve secured to the anode exhaust, a cathode exhaust valve secured to the cathode exhaust, and the coolant loop. 
     
     
       5. The control system of  claim 1 , wherein the water reservoir further comprises pores defined in at least one of a cathode porous body secured in fluid communication with the cathode catalyst surface of the membrane electrode assembly, and an anode porous body secured in fluid communication with the anode catalyst surface of the membrane electrode assembly. 
     
     
       6. The control system of  claim 1 , wherein the water reservoir defines a water-retention volume dimensioned to retain an adequate volume of water to maintain the relative humidity of the reactant streams at or about 1.00 during a predetermined duration of power output of the fuel cell that is between about eighty percent and about one-hundred percent of a predetermined maximum power output of the fuel cell. 
     
     
       7. The control system of  claim 6 , wherein the water reservoir defines a water-retention volume that is adequate to maintain a relative humidity of the reactant streams  16 A,  16 B at or about 1.0 whenever the predetermined duration of the power output of the fuel cell that is between about eighty percent and about one-hundred percent of a predetermined maximum power output of the fuel cell is about five minutes. 
     
     
       8. A method of operating a fuel cell power plant configured to generate electrical current from an oxidant reactant stream and a hydrogen-rich fuel reactant stream to control relative-humidity levels of reactant streams passing through the fuel cell, the fuel cell power plant having a control system according to  claim 1 , the method comprising:
 controlling at least one of: the pressure of the reactant streams; the flow rate of 
 the reactant streams; the temperature of a the coolant fluid passing through the sealed coolant flow field; and a flow rate of the coolant; 
 so that water moves from the water reservoir into at least one of the reactant streams whenever power generated by the fuel cell is between about eighty percent and about one-hundred percent of the predetermined maximum power output of the fuel cell, and so that water moves from the at least one of the reactant streams into the water reservoir whenever power produced by the fuel cell is less than about seventy-five percent of the predetermined maximum power output of the fuel cell. 
 
     
     
       9. The method of  claim 8  further comprising, retaining an adequate volume of water within the water reservoir to maintain the relative-humidity of the at least one of the reactant streams at about 1.00 during a predetermined duration of power output of the fuel cell that is between about eighty percent and about one-hundred percent of a predetermined maximum power output of the fuel cell. 
     
     
       10. The method of  claim 8 , wherein the controlling so that water moves from the at least one of the reactant streams into the water reservoir comprises controlling water to move water into pores defined in at least one of a cathode porous body secured in fluid communication with a cathode catalyst surface of a membrane electrode assembly and an anode porous body secured in fluid communication with an anode catalyst surface of the membrane electrode assembly.